Over the years there have been a wide range of solar roof mounting devices to support solar panels on the roof of buildings. These mounting systems typically incorporate anchor posts or ballasts to hold the solar panel assembly in place on the roof and various solar frames or racks connected to the posts or weights to support and clamp the panels in place. The frames or racks comprise rolled steel or extruded aluminum beams and rails with sheet metal, welded and machined connecting components.
One such solar mounting system is the ballasted type system which utilizes weights, typically in the form of concrete pavers or other common building materials situated in trays that in turn are mounted to framing or strut members that support and hold the solar panels in place (FIG. 1). The main advantages of this type of roof mounting system is that it minimizes the number roof penetrations and evenly distributes the load on the roof. However they suffer from the following disadvantages:                Creates more weight on the roof than other systems        Can cause abrasive damage to the roof due to shift of solar mass due to wind or seismic activity        Low profile us subject to shadowing from other equipment on roof        Does not allow access for re-roofing unless the solar array is completely removed        
Traditional solar support racking structures that anchor to the roof or the roof beams include posts that are anchored by means of fasteners are used widely on all types of roofs. These types of devices provide a light weight alternative to ballasted or weighted systems (FIG. 1). The majority of these types of mounting systems have large numbers of mounts to the roof to better distribute the loads imposed by the solar array. Typically is on average one anchor per panel or approximately one anchor per 15 to 20 square feet of roof area.
Although this type of mounting structure overcomes the first two of the disadvantages noted for ballasted systems it nevertheless has in common the second two disadvantages noted above. In addition to those disadvantages the large number of anchors to the roof create more potential for roof leakage. Additionally, the cost of both creating and subsequently sealing these penetrations substantially increases the cost of these mounted systems.
Alternative solar mounting methods have been developed to overcome the disadvantages noted above. Efforts have been made to minimize the number of mounts on the rooftop required to support the solar systems which have included truss style supports. These truss style systems not only reduce the number of penetrations but also provide the advantage of raising the solar array so that there is less possibility of shadowing by adjacent equipment on the roof. They may also provide better access to roofs for repair and for re-roofing.
Some work has been done over the years to develop cost-effective field deployable truss structures for long span applications. Ignash, U.S. Pat. No. 6,321,521, developed a collapsible 3 sided truss structure that allows the three framework sections to be folded together to form the truss beam. Nygren, U.S. Pat. No. 6,076,770, developed an inwardly foldable truss to reduce space for shipment. Merrifield, U.S. Pat. No. 7,028,442, developed a linearly expandable truss structure that allowed variable length structures. And Beltz, U.S. Pat. No. 4,546,591, developed a truss structure with removable pins to allow the structure to be collapsed.
Although truss style solar mounting structures overcome the disadvantages noted above they suffer from the disadvantage of possibly creating excessive reaction loads at their positions of attachment to the roof beams. These reaction loads can cause substantial bending or twisting of the roof beams to which they are mounted. Building roof structures are designed to withstand gravitational forces and lift forces associated with wind velocity. However roof beam support structures are not designed to withstand excessive bending or twisting of the roof beams.
Bending loads can be transmitted into building structures from the horizontal wind load applied to the tilted panels positioned above the roof. The bending moment is created by a wind load force, F, pushing on the solar array a distance, D, above the roof. The bending load is expressed by the relationship: M=FD, where M is the bending moment applied to the roof beam, caused by the force F applied at a distance D above the roof structure. Because the panels are positioned in an elevation well above the roof line, this bending load can be quite substantial. creating a high bending moment on the roof beam.
The bending load on the posts can be substantially reduced by using a truss structure with the vertex of the truss positioned at the mounting post. By doing this the horizontal force at the elevated panel height can be transmitted through the truss members connected directly to the posts. The bending load is then considerably reduced since the reaction force is now located down at the post instead of at the panel height.
Although the truss support type structure reduces high bending loads caused by elevated panels it suffers from the disadvantage of requiring truss members to be connected between posts to “close the triangle” and eliminate any large horizontal reaction loads at the vertex of each post. These truss members are necessarily connected between adjacent mounting posts to reduce the reaction load. Unfortunately these mounting post connecting truss members get in the way of re-roofing or repairing the roof and it may become necessary to remove the solar system in order to perform these functions at a considerable expense.
A further disadvantage of truss structures is that it is difficult to field modify the tilt angle of the panels to adjust for latitudinal variations or equipment interference and shadowing. Typically truss structures are pre-fabricated and erected in the field with a fixed tilt angles. If a change needs to be made to the tilt angle the prefabricated components will have to be rebuilt to obtain the new tilt angle desired. This absence loss of field tilt adjust flexibility can be a nuisance and time-consuming.
Another disadvantage of truss structures is that the height of the array cannot be adjusted in the field. Most roof structures have variations in height. This height variation can cause shadowing between adjacent arrays. If the height of the array had height adjustment capability this problem could be avoided.
Another disadvantage of truss structures is that the post mounting positions are generally fixed with little allowance for adjusting the spacing. If there are variations in the spacing of the roof beams to which they attached, it may be difficult to accommodate these variations without making modifications to the truss system.
In summary there is a need for a solar mounting structure that eliminates the disadvantages noted above for existing systems and provides the following:                Allows higher elevation for the solar arrays to reduce shading from roof mounted equipment        Minimizes bending stresses on building roof members caused by elevated solar arrays        Minimizes the number of support members required close to the roof that would interfere with re-roofing and require removal        Minimizes the number of posts and resultant roof penetrations        Has field adjust capability to change the tilt angle        Has field adjust capability to modify the height        Has field adjust capability to modify the mounting post positions.        Light weight structure to minimize the gravitational load impact on the roof        Eliminates roof wear and abrasion associated with ballast systems        